oml: Add a missing break switch for NM_OC_BS11

It appears to me that for NM_OC_BS11 mo was either NULL or the
one mo value from NM_OC_BS11_RACK. The break inside the nested
switch case didn't break from the outer one.

Fixes Coverity: CID 1040728

openbsc/src/libcommon/gsm_data_shared.c

@@ -390,6 +390,7 @@ gsm_objclass2mo(struct gsm_bts *bts, uint8_t obj_class,
 		default:
 			return NULL;
 		}
+		break;
 	case NM_OC_BS11_RACK:
 		mo = &bts->bs11.rack.mo;
 		break;